Kata: Roman Numerals

roman_numerals.py

import unittest

def toRoman(n):
    """
    Convert an integer to Roman numerals. Returns an empty string for 0.
    """
    if n == 0:
        return ''
    map = { 1: 'I', 4: 'IV', 5: 'V', 9: 'IX', 10: 'X', 40: 'XL', 50: 'L', 90: 'XC', 100: 'C' }
    key = max(k for k, v in map.iteritems() if k <= n)
    times = n / key
    remainder = n % key
    return map[key] * times + toRoman(remainder)

class TestRomanNumerals(unittest.TestCase):
    def test_zero(self):
        self.assertEqual('', toRoman(0))

    def test_one(self):
        self.assertEqual('I', toRoman(1))

    def test_fity(self):
        self.assertEqual('L', toRoman(50))

    def test_two(self):
        self.assertEqual('II', toRoman(2))

    def test_twenty(self):
        self.assertEqual('XX', toRoman(20))

    def test_four(self):
        self.assertEqual('IV', toRoman(4))

    def test_nineteen(self):
        self.assertEqual('XIX', toRoman(19))

if __name__ == '__main__':
    unittest.main()

roman_numerals.rb

require 'rspec'

def to_roman(n)
  return '' if n.nil? || n == 0
  map = { 1 => 'I', 4 => 'IV', 5 => 'V', 9 => 'IX', 10 => 'X', 40 => 'XL', 50 => 'L', 90 => 'XC', 100 => 'C' }
  base = map.keys.sort.reverse.find { |x| x <= n }
  times, remainder = n.divmod(base)
  map[base] * times + to_roman(remainder)
end

describe 'converting roman numerals' do
  {
    1   => 'I',
    2   => 'II',
    3   => 'III',
    4   => 'IV',
    5   => 'V',
    6   => 'VI',
    9   => 'IX',
    10  => 'X',
    11  => 'XI',
    20  => 'XX',
    25  => 'XXV',
    40  => 'XL',
    49  => 'XLIX',
    50  => 'L',
    90  => 'XC',
    100 => 'C',
    194 => 'CXCIV',
    200 => 'CC'
  }.each do |k, v|
    it "converts #{k} to #{v}" do
      to_roman(k).should == v
    end
  end
end